Commercial quantities of oils are mostly obtained from plants. Non-plant sources of oils are used commercially primarily because oils with different properties, determined by the fatty acids, are available. Oils are also accumulated by some yeasts and filamentous fungi. Of the some 600 different yeast species, only 25 or so are able to accumulate more than 20% lipid (Ratledge, Biochem Soc Trans. 1989;17:1139-41), these are the oleaginous species.
Microbial lipids could contribute to the covering of the increasing demand of fats and oils. In addition, single cell oil (SCO) is of particular interest due to the capacity of oleaginous yeasts to convert numerous raw materials into value-added fats and oils.
Biosynthetic pathways of unsaturated fatty acid of mammalian physiological importance are depicted in FIG. 1. D12-desaturase, D6-desaturase and D15-desaturase, along with other enzymes involved in the conversion of fatty acids, e.g. those described in FIG. 1., are the enzymes of interest to introduce into oleaginous yeast.
Biosynthetic pathways of n-6 and n-3 polyunsaturated fatty acids of mammalian physiological importance are disclosed in FIG. 1. D12-desaturase is responsible for conversion of oleic acid (OA; 18:1, 6) to linoleic acid (LA; 18:2-9,12). D6-desaturase is responsible for conversion of LA to GLA (18:3-6, 9, 12) and of α-linolenic acid (ALA, 18:3-9, 12, 15) to stearidonic acid (SDA, 18:4-6, 9, 12, 15). These enzymes, along with other important enzymes involved in the conversion of fatty acids, e.g. those described in FIG. 1., are the enzymes of interest to introduce into oleaginous yeast.
The attractions of Yarrowia lipolytica as an oleaginous yeast with a capacity for growth on cheap carbon sources such as glucose led us to develop an unsaturated-fatty acid production system that can express exogenous genes involved in lipid biosynthesis.